The best approach (and to me the only that doesn't have crucial flaws) I could think of is still the NIP-29 one: groups are identified by a random id and can have owners and mods and rules, but the rules are enforced by a specific trusted relay. So in fact a group "address" is given by id+relay. If the relay goes offline or become evil groups can just move to a different relay. Anyone can also fork the group by reusing its id but defining a different relay that accepts the new ownership.